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Querying, Changing, and Validating Your Data with Entity Framework Julia Lerman, Rowan Given that a relationship can be represented by up to three properties (two the rest of these properties for you; this is known as relationship fix-up. how to fix-up relationships in poco entities using DetectChanges() method. If we declare all the properties as virtual, change tracking proxies are created and. Oct 22, In Entity Framework, an entity can be related to other entities through . (also known as relationship fix-up) for the POCO entities with proxies.
By Convention So what is configuration by convention? When you follow some simple rules on property types and names, Entity Framework will auto-configure many of the software and database features. Configuring Relationships in Entity Framework Configuring scalar non-relational properties is quite straightforward, but when it comes to entity relationships, it can be more tricky to decide which approach is best for configuring them.
By default, when I delete a Student, I will get a referential integrity error: So how do I fix this? The official Microsoft documentation recommends manually deleting each foreign key for dependent entities: If we look at the documentation for Entity Framework 6 it says that: If a foreign key on the dependent entity is nullable, Code First does not set cascade delete on the relationship, and when the principal is deleted the foreign key will be set to null.
Entity Framework should now set the foreign keys to null for these entities when I delete a student. However as the code stands, I will still get the same referential integrity error. The crucial detail here is that the dependent entities must be loaded before the principal entity is deleted.
Here I explicitly load both the Equipmentand Transaction entities before removing the student entity: When the Equipment and Transaction entities are loaded into the working memory, EF knows to set the relevant dependent entities foreign keys to null. Relationships are tracked through object references instead of foreign key properties.
This type of association is called an independent association. The most common way to modify an independent association is to modify the navigation properties that are generated for each entity that participates in the association. You can choose to use one or both types of associations in your model. However, if you have a pure many-to-many relationship that is connected by a join table that contains only foreign keys, the EF will use an independent association to manage such many-to-many relationship.
- Entity Framework
- Configuring Entity Relationships with Entity Framework
- Relationships, navigation properties and foreign keys
The following image shows a conceptual model that was created with the Entity Framework Designer. The model contains two entities that participate in one-to-many relationship.
Both entities have navigation properties.
Entity Framework Core One To Many Relationships Conventions
Course is the depend entity and has the DepartmentID foreign key property defined. The following code snippet shows the same model that was created with Code First. For information on setting up relationships in your model, see the following pages.
Creating and modifying relationships In a foreign key association, when you change the relationship, the state of a dependent object with an EntityState. Unchanged state changes to EntityState. In an independent relationship, changing the relationship does not update the state of the dependent object. The following examples show how to use the foreign key properties and navigation properties to associate the related objects. With foreign key associations, you can use either method to change, create, or modify relationships.
With independent associations, you cannot use the foreign key property. By assigning a new value to a foreign key property, as in the following example. DepartmentID; The following code removes a relationship by setting the foreign key to null. Note, that the foreign key property must be nullable. Synchronization does not occur because the object context does not contain permanent keys for added objects until they are saved.
If you must have new objects fully synchronized as soon as you set the relationship, use one of the following methods. The following code creates a relationship between a course and a department.
If the objects are attached to the context, the course is also added to the department.
Courses collection, and the corresponding foreign key property on the course object is set to the key property value of the department. If you are working with Entity Framework that is based on.
What triggers Entity Framework to fix up a navigation property? - Stack Overflow
You can also set the current value to null using the following method. For example, you can add an object of type Course to the department. This operation creates a relationship between a particular course and a particular department.
If the objects are attached to the context, the department reference and the foreign key property on the course object will be set to the appropriate department. Add newCourse ; By using the ChangeRelationshipState method to change the state of the specified relationship between two entity objects.